Written by Merel Dagher (PEACE Advisor)

Describe the atmosphere when ecological systems formed roughly 4 billion years ago.a.Oxygen was abundant in the environment b.The conditions were the same as nowc.CO2, NH4+, CH4, and NO were present at high concentrations d.The ozone layer had formed completely Click "Read More" to see the answer.

The correct answer is c. Carbon dioxide, ammonium, methane gas, and nitric oxide were very abundant in the environment, which are highly toxic to humans (we wouldn’t have survived at all in that environment). Oxygen didn’t come into play until about 1 billion years later, thanks to the help of cyanobacteria. The ozone layer formed after the prevalence of oxygen in the environment.